[music-dsp] Envelope Detection and Hilbert Transform

Angelo Farina farina at pcfarina.eng.unipr.it
Thu Sep 23 02:57:07 EDT 2004

The (real) FFT of a real signal does not produce any "negative frequency"
spectrum, it only produces N/2+1 positive frequency spectral lines....
Or are You doing a complex FFT on a real signal? This is really stupid, it
takes more than twice the computational power required for a real FFT...

Angelo Farina

> -----Original Message-----
> From: music-dsp-bounces at ceait.calarts.edu 
> [mailto:music-dsp-bounces at ceait.calarts.edu] On Behalf Of 
> Erik de Castro Lopo
> Sent: 23 September 2004 00:10
> To: a list for musical digital signal processing
> Subject: Re: [music-dsp] Envelope Detection and Hilbert Transform
> On Wed, 22 Sep 2004 14:56:12 -0700
> "Joshua Scholar" <joshscholar at yahoo.com> wrote:
> > 
> > All this talk about windows, does that mean you have a way 
> to use FFTs 
> > to do Hilbert Transforms __other__ than convolution?
> Yes, take the FFT of a signal, which creates a N frequency 
> domain samples, with the up half of the being a reflection of 
> the lower half. Zero out the upper half, do an inverse FFT 
> and viola, you have the analytic version of the original 
> signal (ie its Hilbert transform).
> Erik
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